Fix IsNull pruning expression generation without null_count statist…

…ics (#3044)

datafusion/core/src/physical_optimizer/pruning.rs

@@ -639,7 +639,7 @@ fn build_is_null_column_expr(
         Expr::Column(ref col) => {
             let field = schema.field_with_name(&col.name).ok()?;
 
-            let null_count_field = &Field::new(field.name(), DataType::UInt64, false);
+            let null_count_field = &Field::new(field.name(), DataType::UInt64, true);
             required_columns
                 .null_count_column_expr(col, expr, null_count_field)
                 .map(|null_count_column_expr| {
@@ -809,10 +809,19 @@ mod tests {
     use std::collections::HashMap;
 
     #[derive(Debug)]
-    /// Test for container stats
+
+    /// Mock statistic provider for tests
+    ///
+    /// Each row represents the statistics for a "container" (which
+    /// might represent an entire parquet file, or directory of files,
+    /// or some other collection of data for which we had statistics)
+    ///
+    /// Note All `ArrayRefs` must be the same size.
     struct ContainerStats {
         min: ArrayRef,
         max: ArrayRef,
+        /// Optional values
+        null_counts: Option<ArrayRef>,
     }
 
     impl ContainerStats {
@@ -835,6 +844,7 @@ mod tests {
                         .with_precision_and_scale(precision, scale)
                         .unwrap(),
                 ),
+                null_counts: None,
             }
         }
 
@@ -845,6 +855,7 @@ mod tests {
             Self {
                 min: Arc::new(min.into_iter().collect::<Int64Array>()),
                 max: Arc::new(max.into_iter().collect::<Int64Array>()),
+                null_counts: None,
             }
         }
 
@@ -855,6 +866,7 @@ mod tests {
             Self {
                 min: Arc::new(min.into_iter().collect::<Int32Array>()),
                 max: Arc::new(max.into_iter().collect::<Int32Array>()),
+                null_counts: None,
             }
         }
 
@@ -865,6 +877,7 @@ mod tests {
             Self {
                 min: Arc::new(min.into_iter().collect::<StringArray>()),
                 max: Arc::new(max.into_iter().collect::<StringArray>()),
+                null_counts: None,
             }
         }
 
@@ -875,6 +888,7 @@ mod tests {
             Self {
                 min: Arc::new(min.into_iter().collect::<BooleanArray>()),
                 max: Arc::new(max.into_iter().collect::<BooleanArray>()),
+                null_counts: None,
             }
         }
 
@@ -886,10 +900,29 @@ mod tests {
             Some(self.max.clone())
         }
 
+        fn null_counts(&self) -> Option<ArrayRef> {
+            self.null_counts.clone()
+        }
+
         fn len(&self) -> usize {
             assert_eq!(self.min.len(), self.max.len());
             self.min.len()
         }
+
+        /// Add null counts. There must be the same number of null counts as
+        /// there are containers
+        fn with_null_counts(
+            mut self,
+            counts: impl IntoIterator<Item = Option<i64>>,
+        ) -> Self {
+            // take stats out and update them
+            let null_counts: ArrayRef =
+                Arc::new(counts.into_iter().collect::<Int64Array>());
+
+            assert_eq!(null_counts.len(), self.len());
+            self.null_counts = Some(null_counts);
+            self
+        }
     }
 
     #[derive(Debug, Default)]
@@ -908,8 +941,30 @@ mod tests {
             name: impl Into<String>,
             container_stats: ContainerStats,
         ) -> Self {
-            self.stats
-                .insert(Column::from_name(name.into()), container_stats);
+            let col = Column::from_name(name.into());
+            self.stats.insert(col, container_stats);
+            self
+        }
+
+        /// Add null counts for the specified columm.
+        /// There must be the same number of null counts as
+        /// there are containers
+        fn with_null_counts(
+            mut self,
+            name: impl Into<String>,
+            counts: impl IntoIterator<Item = Option<i64>>,
+        ) -> Self {
+            let col = Column::from_name(name.into());
+
+            // take stats out and update them
+            let container_stats = self
+                .stats
+                .remove(&col)
+                .expect("Can not find stats for column")
+                .with_null_counts(counts);
+
+            // put stats back in
+            self.stats.insert(col, container_stats);
             self
         }
     }
@@ -937,8 +992,11 @@ mod tests {
                 .unwrap_or(0)
         }
 
-        fn null_counts(&self, _column: &Column) -> Option<ArrayRef> {
-            None
+        fn null_counts(&self, column: &Column) -> Option<ArrayRef> {
+            self.stats
+                .get(column)
+                .map(|container_stats| container_stats.null_counts())
+                .unwrap_or(None)
         }
     }
 
@@ -1761,4 +1819,39 @@ mod tests {
         let result = p.prune(&statistics).unwrap();
         assert_eq!(result, expected_ret);
     }
+
+    #[test]
+    fn prune_int32_is_null() {
+        let (schema, statistics) = int32_setup();
+
+        // Expression "i IS NULL" when there are no null statistics,
+        // should all be kept
+        let expected_ret = vec![true, true, true, true, true];
+
+        // i IS NULL, no null statistics
+        let expr = col("i").is_null();
+        let p = PruningPredicate::try_new(expr, schema.clone()).unwrap();
+        let result = p.prune(&statistics).unwrap();
+        assert_eq!(result, expected_ret);
+
+        // provide null counts for each column
+        let statistics = statistics.with_null_counts(
+            "i",
+            vec![
+                Some(0), // no nulls (don't keep)
+                Some(1), // 1 null
+                None,    // unknown nulls
+                None, // unknown nulls (min/max are both null too, like no stats at all)
+                Some(0), // 0 nulls (max=null too which means no known max) (don't keep)
+            ],
+        );
+
+        let expected_ret = vec![false, true, true, true, false];
+
+        // i IS NULL, with actual null statistcs
+        let expr = col("i").is_null();
+        let p = PruningPredicate::try_new(expr, schema).unwrap();
+        let result = p.prune(&statistics).unwrap();
+        assert_eq!(result, expected_ret);
+    }
 }